780 Journal of Medicinal Chemistry, 1975, Vol. 18, No. 8 (15) E. C. Taylor and T. Kobayashi, J . Org. Chem., 38, 2817 (1973). (16) H. G. Mautner, Y.-H. Kim, Y. Gaumont, and R. L. Kisliuk, Abstracts, Pteridine Symposium, Konstanz, Germany, April 1975, in press. (17) J . I. DeGraw, P. Tsakotellis, R. L. Kisliuk, and Y. Gaumont, J . Heterocycl. Chem., 8,105 (1971). (18) A. J . Eisenfeld, H. G. Mautner, and A. D. Welch, Proc. A m . Assoc. Cancer Res., 3,316 (1962).
D u t t a , Tritsch, Cox, Chhedu (19) D. G. Johns, D. Farquhar, M. K. Wolpert, B. A. Chabner, and T. L. Loo, Drug Metab. Dispos.,1,580 (1973). (20) M. Chaykovsky, A. Rosowsky, N. Papathanasopoulos, K. K. Chen, E. J. Modest, R. L. Kisliuk, and Y. Gaumont, J . Med. Chem., 17,1212 (1974). (21) S. B. Horwitz and R. L. Kisliuk. J . Med. Chem., 11, 907 (1968). (22) R. L. Kisliuk, Y. Gaumont, and C. M. Baugh, J . Biol. Chem.. 244,4100 (1974).
Synthesis and Biological Activities of Some IV(Nitro- and -aminobenzyl)adenosinest Shib P. Dutta, George L. Tritsch, Clifford Cox, and Girish B. Chheda* General Clinical Research Center, Department of General Surgery, Roswell Park Memorial Institute, Buffalo, N e w York 24203. Received March 14,1975 Synthesis and biological activities of 1 2 analogs of N 6 -benzyladenosine are described. The compounds were prepared by two methods: (1) direct alkylation of adenosine with an appropriately substituted benzyl bromide to give the N1substituted derivative which was then rearranged in base to give the N6-substituted compound, and (2) by nucleophilic displacement of chlorine in 6-chloropurine ribonucleoside, 6-chloro-2-aminopurine ribonucleoside, and 6chloro-2-aminopurine with an amine. These analogs were examined for their growth inhibitory effect in cultured leukemic cells and also for their effect on adenosine aminohydrolase activity. N6-p-Nitrobenzyladenosine and its 2'deoxy analog were competitive inhibitors (Ki 65, 22 pM).T h e 2-amino-N6-p-nitrobenzyladenine and its ribonucleoside were found to be noncompetitive inhibitors of adenosine aminohydrolase. In cultured L1210 leukemia, 2-amino6-p- nitrobenzylaminopurine and the corresponding ribonucleoside were better growth inhibitors than I@- benzyladenosine, while N6-p-nitrobenzyladenosine,its 2'-deoxy analog, and N6-p-fluorobenzyladenosinewere as active as N6benzyladenosine.
The clinical usefulness of N6-benzyladenosine in neoplastic disease' prompted the synthesis and exploration of the biological activity of nitro and aminobenzyl analogs of this compound. N6-Benzyladenosine has been shown to possess growth inhibitory activity in tumor cell systems in . ~ ~ ~of the N6-benzyladenosine derivvitro and in V ~ V O Some atives have exhibited inhibitory activity toward the uptake of purines and pyrimidines in cultured cells.*x5I t stimulates the growth of tobacco pith tissue in vitro6 and in cell-free systems acts as a competitive inhibitor of adenosine aminohydrolase.' Reported herein are the syntheses of 12 analogs of N6-benzyladenosine, their growth inhibitory properties in three cell lines in culture, and their effect on adenosine aminohydrolase activity. Chemistry. N6-p-Nitrobenzyladenosine (2) was synthesized by a reaction of adenosine with p-nitrobenzyl bromide in DMF to furnish the N1-p-nitrobenzyladenosine derivative. The latter was rearranged in base to give N6-pnitrobenzyladenosine.8 Similarly 0- and m- nitrobenzyladenosine (3 and 4) and p-fluorobenzyladenosine (9) were prepared starting from adenosine and an appropriately substituted benzyl bromide. 2'-Deoxyadenosine was used as the starting material for the preparation of 2'-deoxy-N6-benzyladenosine ( 13)9 and 2'-deoxy-N6-p-nitrobenzyladenosine ( 5 ) . Catalytic reduction of Ne-p-nitrobenzyladenosine gave N6-p-aminobenzyladenosine (7), which was isolated as the HC1 salt. Acetylation of the latter afforded N6-pacetamidobenzyladenosine (8). Reaction of methyl isocyanate with 2',3',5'-tri-O-acetyl-N6-benzyladenosine followed by deacetylation gave a more soluble compound, N- [(9-@D-ribofuranosylpurin-6-yl)-Nbenzylcarbamoyl]methylamine (10). Treatment of N6-benzyladenosine (1)with methanolic hydrogen chloride gave the N6-benzyladenosine hydrochloride (14), which was more soluble in water than the parent compound. However, it was less stable. Nucleophilic displacement of chlorine in 6-chloro-2-aminopurine and 6chloro-2-aminopurine ribonucleoside with p-nitrobenzyl+
This work was supported by U S . Public Health Service Grant CA 14185.
aminelO,ll gave 2-amino-6-p-nitrobenzylaminopurine (12) and 2-amino-6-p-nitrobenzylaminopurineribonucleoside ( 1l),respectively. N6-(2-Methoxy-5-nitro)phenyladenosine (6)was similarly prepared starting from 6-chloropurine ribonucleoside and 2-methoxy-5-nitroaniline. The structures of all these compounds were confirmed by their uv, ir, and NMR spectra as well as from their correct elemental analyses. The physical properties of these analogs are listed in Table I.
Experimental Section Melting points were determined by a Mel-Temp laboratory model melting point apparatus and are uncorrected. Uv spectra were recorded on a Cary 14 and Beckman Acta-V spectrophotometer. NMR spectra were recorded on a Varian A-60A spectrometer in DMSO-ds solution using Me4Si as an internal standard. Elemental analyses were carried out by Heterocyclic Chemical Corporation, Harrisonville, Mo. Homogeneity of all the compounds was checked by thin-layer chromatography in three solvent systems: (a) i-PrOH-concentrated NH40H-HzO (7:1:2 v/v); (b) EtOAc-2ethoxyethanol-16% HCOzH (4:1:2 v/v, upper phase); and (c) EtOAc-n-PrOH-HZ0 (4:1:2 v/v, upper phase). @-p-Nitrobenzyladenosine (2). Method A. T o a solution of 1.33 g of adenosine (5.0 mmol) in 25.0 ml of freshly distilled anhydrous DMF was added 3.24 g (15.0 mmol) of p-nitrobenzyl bromide and the mixture stirred in a stoppered flask a t room temperature for 48 hr. The reaction mixture was then evaporated to dryness in vacuo a t 45O. The gummy residue was triturated three times with 50 ml of hot acetone. The crude residue was dissolved in 50 ml of distilled water and the pH of the solution was adjusted to 9.0-9.5 by careful addition of diluted aqueous NH40H. The mixture was then heated on a steam bath for 3 hr. The pH of the solution was maintained within the range of 9.0-9.5 by addition of diluted aqueous NH40H from time to time. The reaction mixture was evaporated to a small volume and kept a t 4' for 20 hr. A yellow crystalline product was collected on a filter and washed with HzO. Two recrystallizations from absolute EtOH furnished 1.25 g (62.2%) of pure product mp 174-176'; NMR d 8.53 (s, 1,8-H), 8.33 (s, 1, 2-H), 8.27 and 7.67 (pair of doublets, 4, J = 8 Hz in each case, protons of phenyl ring), 5.98 (d, 1, J = 6 Hz,1'-H), 5.43 (d, 2, J = 7 Hz, -CHzC6Hs). Anal. ( C I ~ H ~ ~ N cS, O H,~N. ) w-p-Aminobenzyladenosine Hydrochloride (7). T o a solution of compound 2 (500 mg) in 125 ml of MeOH was added 500
N6-(Nitro-and -arninobenzyl)adenosines
Journal of Medicinal Chemistry, 1975, Vol. 18, No. 8
781
782 Journal of Medicinal Chemistry, 1975, Vol. 18, No. 8
Dutta, Tritsch, Cox, Chheda
Table 11. Biological Activities of Analogs of N6-Benzyladenosine Antiproliferative act, in c u l t u r e b Compd no.
lC 2 3
4 5 6 7 8 9 10 11 12 13
Enzyme' Ki, p.1.l
550 65 530
Nc 37
++,
t +
RPMI 6410
--
at
-+
NA
280'
+
22
i
NA
++
++
+
33
++
+
r
+ ++
a a
80*
+,
NA at 10-i
4001
T ,
i
io
+
+
CD
at lo+ i
L1210
+,
NA at lo-'
+
*
NA ++ at 48 h r , i at 72 h r NA
>++, + at 10'~
>++, + at NA
aKm = 40 r M adenosine. An asterisk after an entry indicates noncompetitive inhibition. Inhibition was competitive in all other instances. Absence of detectable inhibition is indicated by a ,Le., Ki is infinitely large. *Experimental details are in the text. Viable cell density relative to controls is 30-6070, ++; 60-80%, +; 80-90%, f;NA, 90-110"; after 72 hr of incubation at a drug concentration of 10-4 M except where indicated as otherwise. CCompound 1 refers to RiG-benzyladenosine. Structures of all the other compounds correspond to Table I .
mg of 10% Pd/C and the mixture was hydrogenated a t room temperature under atmospheric pressure. The hydrogenation was continued for 16 hr and then the catalyst was removed by filtration. The clear colorless solution was cooled a t -5' and 0.3 ml of 5.2 N HC1-MeOH was added to it and the mixture stirred a t 0' for 1 hr. The solution was then evaporated to dryness a t 40'; the residue was dissolved in 15 ml of anhydrous EtOH, filtered, concentrated to a small volume, and kept a t 0' for 16 hr. The crystalline product was collected on a filter and washed with EtOH. The product was recrystallized once from absolute EtOH: yield 456 mg (89.7%); mp 130-133' dec. Anal. (C17H20Ns04-HCl)C, H, N. N6-p-Acetamidobenzyladenosine (8). To a solution of compound 7 (100 mg) in 10 ml of H20 was added 100 mg of sodium acetate followed by addition of 2 ml of AczO. The mixture was stirred a t room temperature for 2 hr and then carefully neutralized to pH 7.0 by slow addition of 1 N NaOH solution. The neutral solution was allowed to stand a t 4' for 16 hr. The crystalline product was collected on a filter, washed with water, and recrystallized once from absolute EtOH: yield 80 mg (77.3%); mp 212-214'. Anal. (CigH2&"0~0.5Hz0) C, H, N. 2-Amino-6-p-nitrobenzylamino-9(8-D-ribofuranosy1)purine ( 1 1 ) . Method B. T o a suspension of 1.51 g (8.0 mmol) of p-nitrobenzylamine hydrochloride in 30 ml of hot absolute EtOH was added 0.448 g (8.0 mmol) of KOH dissolved in 5 ml of absolute EtOH. A pellet of KOH was held by a pair of tweezer and stirred in this mixture until the deep blue color of p-nitrobenzylamine anion just persisted. Then a few milligrams of p-nitrobenzylamine hydrochloride was added until the yellow color of neutral p-nitrobenzylamine came back. The precipitated KCI was removed by filtration and 1.21 g (4.0 mmol) of 2-amino-6-chloropurine ribonucleoside was added to the filtrate. The reaction mixture was refluxed for 18 hr and then chilled at 4' for 1hr. The dark gummy solid was collected on a filter and repeatedly triturated with hot benzene until it turned into a yellow powder. The crude material was recrystallized twice from absolute EtOH: yield 1.09 g (60.2%); mp 105-106O dec; ir (KBr) max 3400 (OH), 3300 (NH), 1520, 1400, 1340, (NOz), and 1490 cm-' (C=N, C=C). Anal. (C17HlgN70~ 2H20) C, H, N. N-[ (9-~-~-Ribofuranosylpurin-6-yl)-N-benzylcarbamoyllmethylamine (10). Method C. To a solution of 893 mg (2.50 mmol) of N6-benzyladenosine2 (1) in 5 ml of anhydrous pyridine was added 2 ml of AczO and the mixture was stirred a t room temperature for 2 hr. MeOH (5 ml) was then added to the reaction mixture, which was then stirred for another 15 min and then evaporated to dryness. The residue was dissolved in 10 ml of anhydrous pyridine and again evaporated to dryness. The crude product was found to be homogenous by TLC in solvents B and C and it had the same uv spectra as N6-benzyladenosine in water, 0.1 N HCI, and 0.1 N NaOH solutions. The gummy residue was redissolved in 10 ml of anhydrous pyridine and 0.570 g (10 mmol) of methyl iso-
cyanate was added and the mixture was heated a t 90° for 6 hr in a glass bomb with stirring. The reaction mixture was then evaporated to dryness and the last traces of pyridine were removed by repeated azeotropic distillation with anhydrous toluene. The gummy residue was dissolved in 40 ml of 4.0 N NH3-MeOH and the solution stirred a t 4O for 16 hr. A white crystalline product that gradually precipitated was filtered, washed with MeOH, and recrystallized once from absolute EtOH: yield 936 mg (90.4%); mp 165-167O; NMR & 8.75 (s, 1, 8-H), 8.72 (s, 1, 2-H), 7.33 (s, 5 , -CeHs), 6.01 (d, 1, J = 6 Hz, 1'-H), 5.95 (9, 2, -CHzC&,), and 2.92 ppm (d, 3, J = 3 Hz, -NHCH3). Anal. (C1gH22N605)C, H, N. I@-Benzyladenosine Hydrochloride (14). A solution of 1.0 g of N6-benzyladenosine2 (1) (dried under high vacuum a t 100' for 16 hr) in 1000 ml of anhydrous MeOH was cooled to -5' in an icesalt bath and 0.54 ml of 5.2 N HC1-MeOH was added to it. The mixture was stirred at Oo for 1 hr and then evaporated to dryness a t 30'. The residue was dissolved in 25 ml of anhydrous MeOH and the solution was diluted with 250 ml of ether. The precipitated product was collected on a filter, washed with ether, and recrystallized from MeOH-ether: yield 943 mg (83.5%); mp 108-110'; uv h max 265 (0.1 N HCl), 270 (water), and 270 nm (0.1 N NaOH). Anal. (C17H19Ns04.HC1.0.5H20) C, H , N. Enzyme Assay. Adenosine aminohydrolase from calf intestinal mucosa (200 U/mg supplied as a suspension in 3.2 M ammonium sulfate pH 7.5) was obtained from Sigma Chemical Co. This preparation has been subjected to numerous structural s t u d i e ~ ' ~and ~'~ has been used to evaluate the inhibitory properties of large numbers of synthetic purine analog^.'^-'^ It has an isoelectric point of 4.8512 and an invarient K , of about 50 pM adenosine between pH 6 and 10.15 The assay of KalckarZ0as described by KaplanZ1was used to determine enzyme activity in terms of rate of change of absorbance a t 265 nm. Analysis of the kinetic data was performed by means of double reciprocal plots as described by Dixon and Webb.22 The linear regressions were fitted by eye or a computerprogram-generated least-squares fit assuming equal variances for the experimental reaction v e l o c i t i e ~ . ~ ~ Growth Inhibition. Antiproliferative activity was evaluated in cell culture. Cells derived from the buffy coat of a normal individual (Nc 37) and from a patient with myeloblastic leukemia (RPMI 6410), as well as L1210 mouse leukemia cells, were cultured in suspension without agitation in RPMI No. 1640 medium suppleniented with 20% fetal calf serum.24 The tubes were inoculated with cells taken from stock cultures in logarithmic growth to a starting density previously determined to be near the minimum required for logarithmic growth of control cultures. At 24-hr intervals, 0.2 ml was removed and mixed with Trypan Blue to a final concentration of 0.05%, and total and viable cells were counted in a hemocytometer. Cells able to exclude the dye were scored as viable. The compounds were dissolved in DMSO and allowed to remain a t 37' overnight. This achieved sterilization. Sterile medium was then
N6-(Nitro- and -aminobenzyl)adenosines added to bring the concentration of DMSO to 0.5% and that of the compound to M. A t the concentration used, DMSO did not affect the growth of control cultures.
Results and Discussion The highest affinity for the substrate binding site of adenosine aminohydrolase was shown by the competitive inhibitors N6-p-nitrobenzyladenosine(2) and N6-p-nitrobenzyl-2‘-deoxyadenosine( 5 ) (Table 11). For this enzyme, K, may be considered equivalent to the enzyme-substrate dissociation constant.25 This allows comparison of Ki with K,. Thus, our best inhibitor had an affinity for the substrate binding site comparable to the affinity of the enzyme for substrate (K, = 40 &f adenosine). N6-Benzyladenosinez6 (1) and N6-o-nitrobenzyladenosine(3) had lower affinities. The following compounds were noncompetitive inhibitors: N6-m-nitrobenzyladenosine(4), 2-amino-6-pnitrobenzylaminopurine ( 12), and 2-amino-6-p-nitrobenzylaminopurine ribonucleoside (11). The basis for lack of binding of compounds 6-9 is not clear, but it is suggested that since N6-p-aminobenzyladenosine(7) is not bound while the p-nitro compound 2 is a good inhibitor, that the alteration in electron distribution in the benzene ring produced by an electron-withdrawing group, i.e., Nos, favors prebinding while an electron-donating group, i.e., “2, vents it. On this basis, the poor binding of N6-o-nitrobenzyladenosine (3) must be attributed to steric factors. In order to possibly improve upon the antitumor activity of N6-benzyladenosine (I), several modifications were made in the benzene ring and in the purine moiety of the compound (Table 11). The N6-p-nitrobenzyladenosine(2) and its 2‘-deoxy analog 5 and the N6-m-nitrobenzyladenosine (4) were as potent as the parent compound in L1210 leukemia cell line while in the Nc 37 and RPMI 6410, the compounds were less active than the parent compound. The 2’-deoxy-N6-benzyladenosine (13) and N6-o-nitrobenzyladenosine (3) were almost inactive. The 2-amino-6-pnitrobenzylaminopurine (12) and the corresponding ribonucleoside 11 were better growth inhibitors of L1210 cells than the parent compound, N6- benzyladenosine (1). The 1v6-(2-methoxy-5-nitropheny1)adenosine (6) was also active in L1210 cells. N6-p- Aminobenzyladenosine (7) and its Nacetyl derivative 8 were less active than the parent N6-benzyladenosine in three cell lines. N6-p-Fluorobenzyladenosine (9) was also active in the same range as the parent compound in L1210 leukemia. As adjuvants to 8-0-arabinofuranosyladenine (Ara-A) chemotherapy in cancer, the enzyme inhibitors like Ne-pnitrobenzyladenosine (2) and the corresponding 2‘-deoxy analog 5 are of interest. Compounds of this type can be used, in high enough dosage levels because of their relative
Journal of Medicinal Chemistry, 1975, Vol. 18, No. 8 783
nontoxic nature, to protect Ara-A from being deaminated in vivo to the inactive arabinosyl hypoxanthine by adenosine aminohydrolase. In vivo evaluation of these compounds is in progress.
Acknowledgments. We wish to thank Drs. A. Mittelman, G. P. Murphy, and E. D.Holyoke for their keen interest and encouragement in this work. References and Notes (1) A. Mittelman, J. T. Evans, and A. Brugarolas, Proc. Am. Assoc. Cancer Res., 15,517 (1974). (2) M. H. Fleysher, A. Bloch, M. T. Hakala, and C. A. Nichol, J . Med. Chem., 12,1056 (1969). (3) Y. Rustum, T. Al-Hussainy, C. Cimpson, and E. Mihich, Proc. Am. Assoc. Cancer Res., 14,269 (1973). (4) J. F. Henderson, A. R. P. Paterson, I. C. Caldwell, B. Paul, M. C. Chan, and K. F. Lau, Cancer Chemother. Rep., Part 2, 3, 71 (1972). (5) M. T. Hakala, G. B. Chheda, and L. N. Kenny, Abstracts of the 162nd Meeting of the American Chemical Society, Chicago, Ill., August 1973,BIOL 233. (6) N. J. Leonard, S. Achmatowicz, R. N. Loeppky, K. L. Carraway, W. A. Grimm, A. Szweykowska, H. Q.Hamzi, and F. Skoog, Proc. Natl. Acad. Sci. U S A . , 56,709 (1966). (7) S. P. Dutta, G. L. Tritsch, A. Mittelman, and G. B. Chheda, Fed. Proc., Fed. Am. SOC.Exp. Biol., 33 (Part 11), 1234 (1974). (8) J. W. Jones and R. K. Robins, J. Am. Chem. SOC.,85, 193 (1963). (9) M. J. Robins and E/ M. Trip, Biochemistry, 12,2179 (1973). (10) A. Galat and G. Elion, J. Am. Chem. SOC.,61,3585 (1939). (11) J. Graymore, J. Chem. SOC.,1116 (1947). (12) P. M.Murphy, M. Noonan, P. Collins, E. Tully, and T. G. Brady, Biochem. Biophys. Acta, 171,157 (1969). (13) T. G. Brady and W. O’Connell, Biochem. Biophys. Acta, 62, 216 (1962). (14) H. J. Schaeffer in “Drug Design”, Vol. 11, E. J. Ariens, Ed., Academic Press, New York, N.Y., 1971,p 129. (15) A. Hampton, P. J. Harper, and T. Sasaki, Biochemistry, 11, 4736 (1972). (16) L. M.Lerner and R. R. Rossi, Biochemistry, 11,2772 (1972). (17) B. M. Chaesy and R. J. Suhadolnik, J. Biol. Chem., 242, 3655 (1967). (18) H. P. Baer, G. I. Drummond, and J. Gillis, Arch. Biochem. Biophys., 123,172 (1968). (19) S. Frederiken, Arch. Biochem. Biophys., 113,383 (1966). (20) H.M. Kalckar, J.Biol. Chem., 167,445 (1947). (21) N. 0.Kaplan, Methods Enzymol., 2,473 (1955). (22) M. Dixon and E. C. Webb, “Enzymes”, Academic Press, New York, N.Y., 1964,p 315. (23) W. W. Cleland, Adu. Enzymol., 29,l (1967). (24) C. I. Hong, G. B. Chheda, S. P. Dutta, A. O’Grady-Curtis, and G. L. Tritsch, J. Med. Chem., 16,139 (1973). (25) G. L. Tritsch, Arch. Biochem. Biophys., 161,698 (1974). (26) No explanation can be offered at this point for the reported” inactivity of the N6-benzyladenosine toward this enzyme.
D u t t a , Tritsch, Cox, Chhedu (19) D. G. Johns, D. Farquhar, M. K. Wolpert, B. A. Chabner, and T. L. Loo, Drug Metab. Dispos.,1,580 (1973). (20) M. Chaykovsky, A. Rosowsky, N. Papathanasopoulos, K. K. Chen, E. J. Modest, R. L. Kisliuk, and Y. Gaumont, J . Med. Chem., 17,1212 (1974). (21) S. B. Horwitz and R. L. Kisliuk. J . Med. Chem., 11, 907 (1968). (22) R. L. Kisliuk, Y. Gaumont, and C. M. Baugh, J . Biol. Chem.. 244,4100 (1974).
Synthesis and Biological Activities of Some IV(Nitro- and -aminobenzyl)adenosinest Shib P. Dutta, George L. Tritsch, Clifford Cox, and Girish B. Chheda* General Clinical Research Center, Department of General Surgery, Roswell Park Memorial Institute, Buffalo, N e w York 24203. Received March 14,1975 Synthesis and biological activities of 1 2 analogs of N 6 -benzyladenosine are described. The compounds were prepared by two methods: (1) direct alkylation of adenosine with an appropriately substituted benzyl bromide to give the N1substituted derivative which was then rearranged in base to give the N6-substituted compound, and (2) by nucleophilic displacement of chlorine in 6-chloropurine ribonucleoside, 6-chloro-2-aminopurine ribonucleoside, and 6chloro-2-aminopurine with an amine. These analogs were examined for their growth inhibitory effect in cultured leukemic cells and also for their effect on adenosine aminohydrolase activity. N6-p-Nitrobenzyladenosine and its 2'deoxy analog were competitive inhibitors (Ki 65, 22 pM).T h e 2-amino-N6-p-nitrobenzyladenine and its ribonucleoside were found to be noncompetitive inhibitors of adenosine aminohydrolase. In cultured L1210 leukemia, 2-amino6-p- nitrobenzylaminopurine and the corresponding ribonucleoside were better growth inhibitors than I@- benzyladenosine, while N6-p-nitrobenzyladenosine,its 2'-deoxy analog, and N6-p-fluorobenzyladenosinewere as active as N6benzyladenosine.
The clinical usefulness of N6-benzyladenosine in neoplastic disease' prompted the synthesis and exploration of the biological activity of nitro and aminobenzyl analogs of this compound. N6-Benzyladenosine has been shown to possess growth inhibitory activity in tumor cell systems in . ~ ~ ~of the N6-benzyladenosine derivvitro and in V ~ V O Some atives have exhibited inhibitory activity toward the uptake of purines and pyrimidines in cultured cells.*x5I t stimulates the growth of tobacco pith tissue in vitro6 and in cell-free systems acts as a competitive inhibitor of adenosine aminohydrolase.' Reported herein are the syntheses of 12 analogs of N6-benzyladenosine, their growth inhibitory properties in three cell lines in culture, and their effect on adenosine aminohydrolase activity. Chemistry. N6-p-Nitrobenzyladenosine (2) was synthesized by a reaction of adenosine with p-nitrobenzyl bromide in DMF to furnish the N1-p-nitrobenzyladenosine derivative. The latter was rearranged in base to give N6-pnitrobenzyladenosine.8 Similarly 0- and m- nitrobenzyladenosine (3 and 4) and p-fluorobenzyladenosine (9) were prepared starting from adenosine and an appropriately substituted benzyl bromide. 2'-Deoxyadenosine was used as the starting material for the preparation of 2'-deoxy-N6-benzyladenosine ( 13)9 and 2'-deoxy-N6-p-nitrobenzyladenosine ( 5 ) . Catalytic reduction of Ne-p-nitrobenzyladenosine gave N6-p-aminobenzyladenosine (7), which was isolated as the HC1 salt. Acetylation of the latter afforded N6-pacetamidobenzyladenosine (8). Reaction of methyl isocyanate with 2',3',5'-tri-O-acetyl-N6-benzyladenosine followed by deacetylation gave a more soluble compound, N- [(9-@D-ribofuranosylpurin-6-yl)-Nbenzylcarbamoyl]methylamine (10). Treatment of N6-benzyladenosine (1)with methanolic hydrogen chloride gave the N6-benzyladenosine hydrochloride (14), which was more soluble in water than the parent compound. However, it was less stable. Nucleophilic displacement of chlorine in 6-chloro-2-aminopurine and 6chloro-2-aminopurine ribonucleoside with p-nitrobenzyl+
This work was supported by U S . Public Health Service Grant CA 14185.
aminelO,ll gave 2-amino-6-p-nitrobenzylaminopurine (12) and 2-amino-6-p-nitrobenzylaminopurineribonucleoside ( 1l),respectively. N6-(2-Methoxy-5-nitro)phenyladenosine (6)was similarly prepared starting from 6-chloropurine ribonucleoside and 2-methoxy-5-nitroaniline. The structures of all these compounds were confirmed by their uv, ir, and NMR spectra as well as from their correct elemental analyses. The physical properties of these analogs are listed in Table I.
Experimental Section Melting points were determined by a Mel-Temp laboratory model melting point apparatus and are uncorrected. Uv spectra were recorded on a Cary 14 and Beckman Acta-V spectrophotometer. NMR spectra were recorded on a Varian A-60A spectrometer in DMSO-ds solution using Me4Si as an internal standard. Elemental analyses were carried out by Heterocyclic Chemical Corporation, Harrisonville, Mo. Homogeneity of all the compounds was checked by thin-layer chromatography in three solvent systems: (a) i-PrOH-concentrated NH40H-HzO (7:1:2 v/v); (b) EtOAc-2ethoxyethanol-16% HCOzH (4:1:2 v/v, upper phase); and (c) EtOAc-n-PrOH-HZ0 (4:1:2 v/v, upper phase). @-p-Nitrobenzyladenosine (2). Method A. T o a solution of 1.33 g of adenosine (5.0 mmol) in 25.0 ml of freshly distilled anhydrous DMF was added 3.24 g (15.0 mmol) of p-nitrobenzyl bromide and the mixture stirred in a stoppered flask a t room temperature for 48 hr. The reaction mixture was then evaporated to dryness in vacuo a t 45O. The gummy residue was triturated three times with 50 ml of hot acetone. The crude residue was dissolved in 50 ml of distilled water and the pH of the solution was adjusted to 9.0-9.5 by careful addition of diluted aqueous NH40H. The mixture was then heated on a steam bath for 3 hr. The pH of the solution was maintained within the range of 9.0-9.5 by addition of diluted aqueous NH40H from time to time. The reaction mixture was evaporated to a small volume and kept a t 4' for 20 hr. A yellow crystalline product was collected on a filter and washed with HzO. Two recrystallizations from absolute EtOH furnished 1.25 g (62.2%) of pure product mp 174-176'; NMR d 8.53 (s, 1,8-H), 8.33 (s, 1, 2-H), 8.27 and 7.67 (pair of doublets, 4, J = 8 Hz in each case, protons of phenyl ring), 5.98 (d, 1, J = 6 Hz,1'-H), 5.43 (d, 2, J = 7 Hz, -CHzC6Hs). Anal. ( C I ~ H ~ ~ N cS, O H,~N. ) w-p-Aminobenzyladenosine Hydrochloride (7). T o a solution of compound 2 (500 mg) in 125 ml of MeOH was added 500
N6-(Nitro-and -arninobenzyl)adenosines
Journal of Medicinal Chemistry, 1975, Vol. 18, No. 8
781
782 Journal of Medicinal Chemistry, 1975, Vol. 18, No. 8
Dutta, Tritsch, Cox, Chheda
Table 11. Biological Activities of Analogs of N6-Benzyladenosine Antiproliferative act, in c u l t u r e b Compd no.
lC 2 3
4 5 6 7 8 9 10 11 12 13
Enzyme' Ki, p.1.l
550 65 530
Nc 37
++,
t +
RPMI 6410
--
at
-+
NA
280'
+
22
i
NA
++
++
+
33
++
+
r
+ ++
a a
80*
+,
NA at 10-i
4001
T ,
i
io
+
+
CD
at lo+ i
L1210
+,
NA at lo-'
+
*
NA ++ at 48 h r , i at 72 h r NA
>++, + at 10'~
>++, + at NA
aKm = 40 r M adenosine. An asterisk after an entry indicates noncompetitive inhibition. Inhibition was competitive in all other instances. Absence of detectable inhibition is indicated by a ,Le., Ki is infinitely large. *Experimental details are in the text. Viable cell density relative to controls is 30-6070, ++; 60-80%, +; 80-90%, f;NA, 90-110"; after 72 hr of incubation at a drug concentration of 10-4 M except where indicated as otherwise. CCompound 1 refers to RiG-benzyladenosine. Structures of all the other compounds correspond to Table I .
mg of 10% Pd/C and the mixture was hydrogenated a t room temperature under atmospheric pressure. The hydrogenation was continued for 16 hr and then the catalyst was removed by filtration. The clear colorless solution was cooled a t -5' and 0.3 ml of 5.2 N HC1-MeOH was added to it and the mixture stirred a t 0' for 1 hr. The solution was then evaporated to dryness a t 40'; the residue was dissolved in 15 ml of anhydrous EtOH, filtered, concentrated to a small volume, and kept a t 0' for 16 hr. The crystalline product was collected on a filter and washed with EtOH. The product was recrystallized once from absolute EtOH: yield 456 mg (89.7%); mp 130-133' dec. Anal. (C17H20Ns04-HCl)C, H, N. N6-p-Acetamidobenzyladenosine (8). To a solution of compound 7 (100 mg) in 10 ml of H20 was added 100 mg of sodium acetate followed by addition of 2 ml of AczO. The mixture was stirred a t room temperature for 2 hr and then carefully neutralized to pH 7.0 by slow addition of 1 N NaOH solution. The neutral solution was allowed to stand a t 4' for 16 hr. The crystalline product was collected on a filter, washed with water, and recrystallized once from absolute EtOH: yield 80 mg (77.3%); mp 212-214'. Anal. (CigH2&"0~0.5Hz0) C, H, N. 2-Amino-6-p-nitrobenzylamino-9(8-D-ribofuranosy1)purine ( 1 1 ) . Method B. T o a suspension of 1.51 g (8.0 mmol) of p-nitrobenzylamine hydrochloride in 30 ml of hot absolute EtOH was added 0.448 g (8.0 mmol) of KOH dissolved in 5 ml of absolute EtOH. A pellet of KOH was held by a pair of tweezer and stirred in this mixture until the deep blue color of p-nitrobenzylamine anion just persisted. Then a few milligrams of p-nitrobenzylamine hydrochloride was added until the yellow color of neutral p-nitrobenzylamine came back. The precipitated KCI was removed by filtration and 1.21 g (4.0 mmol) of 2-amino-6-chloropurine ribonucleoside was added to the filtrate. The reaction mixture was refluxed for 18 hr and then chilled at 4' for 1hr. The dark gummy solid was collected on a filter and repeatedly triturated with hot benzene until it turned into a yellow powder. The crude material was recrystallized twice from absolute EtOH: yield 1.09 g (60.2%); mp 105-106O dec; ir (KBr) max 3400 (OH), 3300 (NH), 1520, 1400, 1340, (NOz), and 1490 cm-' (C=N, C=C). Anal. (C17HlgN70~ 2H20) C, H, N. N-[ (9-~-~-Ribofuranosylpurin-6-yl)-N-benzylcarbamoyllmethylamine (10). Method C. To a solution of 893 mg (2.50 mmol) of N6-benzyladenosine2 (1) in 5 ml of anhydrous pyridine was added 2 ml of AczO and the mixture was stirred a t room temperature for 2 hr. MeOH (5 ml) was then added to the reaction mixture, which was then stirred for another 15 min and then evaporated to dryness. The residue was dissolved in 10 ml of anhydrous pyridine and again evaporated to dryness. The crude product was found to be homogenous by TLC in solvents B and C and it had the same uv spectra as N6-benzyladenosine in water, 0.1 N HCI, and 0.1 N NaOH solutions. The gummy residue was redissolved in 10 ml of anhydrous pyridine and 0.570 g (10 mmol) of methyl iso-
cyanate was added and the mixture was heated a t 90° for 6 hr in a glass bomb with stirring. The reaction mixture was then evaporated to dryness and the last traces of pyridine were removed by repeated azeotropic distillation with anhydrous toluene. The gummy residue was dissolved in 40 ml of 4.0 N NH3-MeOH and the solution stirred a t 4O for 16 hr. A white crystalline product that gradually precipitated was filtered, washed with MeOH, and recrystallized once from absolute EtOH: yield 936 mg (90.4%); mp 165-167O; NMR & 8.75 (s, 1, 8-H), 8.72 (s, 1, 2-H), 7.33 (s, 5 , -CeHs), 6.01 (d, 1, J = 6 Hz, 1'-H), 5.95 (9, 2, -CHzC&,), and 2.92 ppm (d, 3, J = 3 Hz, -NHCH3). Anal. (C1gH22N605)C, H, N. I@-Benzyladenosine Hydrochloride (14). A solution of 1.0 g of N6-benzyladenosine2 (1) (dried under high vacuum a t 100' for 16 hr) in 1000 ml of anhydrous MeOH was cooled to -5' in an icesalt bath and 0.54 ml of 5.2 N HC1-MeOH was added to it. The mixture was stirred at Oo for 1 hr and then evaporated to dryness a t 30'. The residue was dissolved in 25 ml of anhydrous MeOH and the solution was diluted with 250 ml of ether. The precipitated product was collected on a filter, washed with ether, and recrystallized from MeOH-ether: yield 943 mg (83.5%); mp 108-110'; uv h max 265 (0.1 N HCl), 270 (water), and 270 nm (0.1 N NaOH). Anal. (C17H19Ns04.HC1.0.5H20) C, H , N. Enzyme Assay. Adenosine aminohydrolase from calf intestinal mucosa (200 U/mg supplied as a suspension in 3.2 M ammonium sulfate pH 7.5) was obtained from Sigma Chemical Co. This preparation has been subjected to numerous structural s t u d i e ~ ' ~and ~'~ has been used to evaluate the inhibitory properties of large numbers of synthetic purine analog^.'^-'^ It has an isoelectric point of 4.8512 and an invarient K , of about 50 pM adenosine between pH 6 and 10.15 The assay of KalckarZ0as described by KaplanZ1was used to determine enzyme activity in terms of rate of change of absorbance a t 265 nm. Analysis of the kinetic data was performed by means of double reciprocal plots as described by Dixon and Webb.22 The linear regressions were fitted by eye or a computerprogram-generated least-squares fit assuming equal variances for the experimental reaction v e l o c i t i e ~ . ~ ~ Growth Inhibition. Antiproliferative activity was evaluated in cell culture. Cells derived from the buffy coat of a normal individual (Nc 37) and from a patient with myeloblastic leukemia (RPMI 6410), as well as L1210 mouse leukemia cells, were cultured in suspension without agitation in RPMI No. 1640 medium suppleniented with 20% fetal calf serum.24 The tubes were inoculated with cells taken from stock cultures in logarithmic growth to a starting density previously determined to be near the minimum required for logarithmic growth of control cultures. At 24-hr intervals, 0.2 ml was removed and mixed with Trypan Blue to a final concentration of 0.05%, and total and viable cells were counted in a hemocytometer. Cells able to exclude the dye were scored as viable. The compounds were dissolved in DMSO and allowed to remain a t 37' overnight. This achieved sterilization. Sterile medium was then
N6-(Nitro- and -aminobenzyl)adenosines added to bring the concentration of DMSO to 0.5% and that of the compound to M. A t the concentration used, DMSO did not affect the growth of control cultures.
Results and Discussion The highest affinity for the substrate binding site of adenosine aminohydrolase was shown by the competitive inhibitors N6-p-nitrobenzyladenosine(2) and N6-p-nitrobenzyl-2‘-deoxyadenosine( 5 ) (Table 11). For this enzyme, K, may be considered equivalent to the enzyme-substrate dissociation constant.25 This allows comparison of Ki with K,. Thus, our best inhibitor had an affinity for the substrate binding site comparable to the affinity of the enzyme for substrate (K, = 40 &f adenosine). N6-Benzyladenosinez6 (1) and N6-o-nitrobenzyladenosine(3) had lower affinities. The following compounds were noncompetitive inhibitors: N6-m-nitrobenzyladenosine(4), 2-amino-6-pnitrobenzylaminopurine ( 12), and 2-amino-6-p-nitrobenzylaminopurine ribonucleoside (11). The basis for lack of binding of compounds 6-9 is not clear, but it is suggested that since N6-p-aminobenzyladenosine(7) is not bound while the p-nitro compound 2 is a good inhibitor, that the alteration in electron distribution in the benzene ring produced by an electron-withdrawing group, i.e., Nos, favors prebinding while an electron-donating group, i.e., “2, vents it. On this basis, the poor binding of N6-o-nitrobenzyladenosine (3) must be attributed to steric factors. In order to possibly improve upon the antitumor activity of N6-benzyladenosine (I), several modifications were made in the benzene ring and in the purine moiety of the compound (Table 11). The N6-p-nitrobenzyladenosine(2) and its 2‘-deoxy analog 5 and the N6-m-nitrobenzyladenosine (4) were as potent as the parent compound in L1210 leukemia cell line while in the Nc 37 and RPMI 6410, the compounds were less active than the parent compound. The 2’-deoxy-N6-benzyladenosine (13) and N6-o-nitrobenzyladenosine (3) were almost inactive. The 2-amino-6-pnitrobenzylaminopurine (12) and the corresponding ribonucleoside 11 were better growth inhibitors of L1210 cells than the parent compound, N6- benzyladenosine (1). The 1v6-(2-methoxy-5-nitropheny1)adenosine (6) was also active in L1210 cells. N6-p- Aminobenzyladenosine (7) and its Nacetyl derivative 8 were less active than the parent N6-benzyladenosine in three cell lines. N6-p-Fluorobenzyladenosine (9) was also active in the same range as the parent compound in L1210 leukemia. As adjuvants to 8-0-arabinofuranosyladenine (Ara-A) chemotherapy in cancer, the enzyme inhibitors like Ne-pnitrobenzyladenosine (2) and the corresponding 2‘-deoxy analog 5 are of interest. Compounds of this type can be used, in high enough dosage levels because of their relative
Journal of Medicinal Chemistry, 1975, Vol. 18, No. 8 783
nontoxic nature, to protect Ara-A from being deaminated in vivo to the inactive arabinosyl hypoxanthine by adenosine aminohydrolase. In vivo evaluation of these compounds is in progress.
Acknowledgments. We wish to thank Drs. A. Mittelman, G. P. Murphy, and E. D.Holyoke for their keen interest and encouragement in this work. References and Notes (1) A. Mittelman, J. T. Evans, and A. Brugarolas, Proc. Am. Assoc. Cancer Res., 15,517 (1974). (2) M. H. Fleysher, A. Bloch, M. T. Hakala, and C. A. Nichol, J . Med. Chem., 12,1056 (1969). (3) Y. Rustum, T. Al-Hussainy, C. Cimpson, and E. Mihich, Proc. Am. Assoc. Cancer Res., 14,269 (1973). (4) J. F. Henderson, A. R. P. Paterson, I. C. Caldwell, B. Paul, M. C. Chan, and K. F. Lau, Cancer Chemother. Rep., Part 2, 3, 71 (1972). (5) M. T. Hakala, G. B. Chheda, and L. N. Kenny, Abstracts of the 162nd Meeting of the American Chemical Society, Chicago, Ill., August 1973,BIOL 233. (6) N. J. Leonard, S. Achmatowicz, R. N. Loeppky, K. L. Carraway, W. A. Grimm, A. Szweykowska, H. Q.Hamzi, and F. Skoog, Proc. Natl. Acad. Sci. U S A . , 56,709 (1966). (7) S. P. Dutta, G. L. Tritsch, A. Mittelman, and G. B. Chheda, Fed. Proc., Fed. Am. SOC.Exp. Biol., 33 (Part 11), 1234 (1974). (8) J. W. Jones and R. K. Robins, J. Am. Chem. SOC.,85, 193 (1963). (9) M. J. Robins and E/ M. Trip, Biochemistry, 12,2179 (1973). (10) A. Galat and G. Elion, J. Am. Chem. SOC.,61,3585 (1939). (11) J. Graymore, J. Chem. SOC.,1116 (1947). (12) P. M.Murphy, M. Noonan, P. Collins, E. Tully, and T. G. Brady, Biochem. Biophys. Acta, 171,157 (1969). (13) T. G. Brady and W. O’Connell, Biochem. Biophys. Acta, 62, 216 (1962). (14) H. J. Schaeffer in “Drug Design”, Vol. 11, E. J. Ariens, Ed., Academic Press, New York, N.Y., 1971,p 129. (15) A. Hampton, P. J. Harper, and T. Sasaki, Biochemistry, 11, 4736 (1972). (16) L. M.Lerner and R. R. Rossi, Biochemistry, 11,2772 (1972). (17) B. M. Chaesy and R. J. Suhadolnik, J. Biol. Chem., 242, 3655 (1967). (18) H. P. Baer, G. I. Drummond, and J. Gillis, Arch. Biochem. Biophys., 123,172 (1968). (19) S. Frederiken, Arch. Biochem. Biophys., 113,383 (1966). (20) H.M. Kalckar, J.Biol. Chem., 167,445 (1947). (21) N. 0.Kaplan, Methods Enzymol., 2,473 (1955). (22) M. Dixon and E. C. Webb, “Enzymes”, Academic Press, New York, N.Y., 1964,p 315. (23) W. W. Cleland, Adu. Enzymol., 29,l (1967). (24) C. I. Hong, G. B. Chheda, S. P. Dutta, A. O’Grady-Curtis, and G. L. Tritsch, J. Med. Chem., 16,139 (1973). (25) G. L. Tritsch, Arch. Biochem. Biophys., 161,698 (1974). (26) No explanation can be offered at this point for the reported” inactivity of the N6-benzyladenosine toward this enzyme.
